Various standards exist in relation to electrical panels and control functions, including the ANSI Control Reliability Standard, ANSI-B11.10. This standard has been in place for many years, and has yet to be truly modernized. One reason is that, since traditional systems function adequately in most circumstances, there is little incentive to introduce the latest technologies, particularly in view of that fact that these systems involve safety-related functions.
One area in need of updating, for example, is the “Lock-Out” function, which simply refers to the right of one individual to lockout others from reinstating power to equipment while they work on that equipment. This is a safety measure, similar to “pulling a meter” on a residence or business. The switches associated with this function are lockable, typically with a padlock, thereby informing maintenance personnel that the panel is now dead. There are times when the reverse is required; that is, where as a trades-person needs to work on a live panel. This is achieved by turning the power back on once the door is open. Switching power on with the door open can, and has, caused personnel injuries.
The disconnect switch is mechanically coupled to a pull-down handle used to interrupt power to the entire panel. A mechanical lock, such as a padlock is installed on the disconnect handle when the handle is pulled down. Although this arrangement now meets consensus standards, but is often not followed and is very inconvenient.
Another area in need of improvement is the emergency stop or “E-Stop” used to interrupt power provided by such panels to certain pieces of equipment, as might be found on the factory floor. For many years, such emergency stopping was accomplished with a master relay wired to interrupt power, much like a switch controlling a saw. One problem with such an arrangement is that if someone running a saw presses the E-Stop button, the starter contacts are welded closed due to a short circuit. This would be considered a system failure and the E-Stop button will not work as intended. The button itself. may be defective, thus, the very purpose of having an E-Stop is defeated. The inability of the E-button to perform as anticipated can result in a very dangerous situation, including the possible loss of life.
Most E-Stop configurations today follow a consensus standard of control reliability requiring redundant switches that are self-checking, adding a very high level of reliability to the control side of the circuit. This is accomplished through the use of safety relays. However, even using the most recent technology, known as safety PLCs, the potential power remains. Also in many situations the emergency stop button is used to halt the flow of electricity for non-emergency reasons, such as operator break periods.
A further need of improvement is panel access in general. Currently anyone can obtain access to a control panel; all that is needed is a screwdriver to open the panel door. Many mechanical door interlocks are broken and require no tools to open panel doors. In many factories people use these private areas to put their lunches, radios, and other personnel items in live control panels containing typical 480-volt, 3-phase power. Nevertheless, traditional panel door hardware techniques are employed.
Accordingly, the need remains for an improved electrical panel access and control technology, preferably one which includes true emergency stop, automated power buss lockout, and other advanced functions.